1. Field of the Invention
The present invention relates to a printing method, and to a printing apparatus including a stencil printing apparatus or the like.
2. Description of the Related Art
A digital thermosensitive stencil printing apparatus is a conventionally known type of printing apparatus that uses a simple printing method. In an apparatus of this type, a thermal head comprising a large number of minute exothermic elements is brought into contact with a master comprising a thermoplastic resin film adhered to a porous substrate and, after a perforation image is thermally fused in the thermoplastic resin of the master in accordance with image information to form a perforated printed plate as a result of a pulsating current being caused to flow to these exothermic elements while the master is being conveyed by conveyance means such as a platen roller, the printed master is wound around the outer circumferential surface of a plate cylinder of a printing drum in which a porous cylindrical plate cylinder is provided as the outer circumferential portion, a printing paper serving as a printing medium is pressed by pressing means against the outer circumferential surface of the plate cylinder, and ink is exuded through perforations on the plate cylinder and through the perforations of the master is transferred onto the printing paper to form a printed image on the printing paper (see, for example, Japanese Laid-Open Patent Publication Nos. H8-216381 and 2002-361994).
Hereinafter in the specification, reference to the plate cylinder shall include the printing drum, and the printing paper shall be referred to simply as “paper”.
However, in printing carried out using a stencil printing apparatus as described above employing the same printed master, the position of the master clamped onto and wrappingly held around the plate cylinder gradually displacements in the direction of rotation of the plate cylinder as the copy number increases over the course of the printing. Printing carried out with this “master position displacement” state unnoticed leads to printed image position displacement with respect to the paper in the paper conveyance direction (hereinafter also referred to as the “top-bottom direction”). Printed image position on the paper is confirmed only upon completion of the printing and, accordingly, printed image displacement is revealed only when the printing is already finished.
Furthermore, gradual position displacement of the printed image (hereinafter also referred to as “printing position displacement”) occurs for a different reason in printing carried out using a stencil printing apparatus as described above employing the same printed master. That is to say, a phenomenon known as “master stretch” in which the master clamped onto the plate cylinder gradually stretches occurs as the copy number increases. Printing position displacement due to master stretch necessitates reprinting.
Because the printing position displacement caused by the master position displacement described above requires reprinting and, as a result, necessitates further plate making and additional printing on paper employing the new printed master, the time taken therefor, as well as the master employed for the plate making and the paper employed for the printing, is wasted.